“There was no guarantee that he would be found but a three-and-a-half hour opportunity was missing.”

CCTV footage on the day showed Mr Howe making his way in to the lounge area at 3.20pm.

At 3.23pm he was shown climbing over the perimeter fence, having gone through the patio doors.

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Mr Howe's next and last confirmed sighting was on Waterloo Road, in Middlesbrough, where he visited Waterloo News.

He was then seen making his way in the direction of Woodlands Road.

His body was discovered early the next morning by a dog walker.

A post-mortem examination report prepared by Dr Jan William Lowe revealed that Mr Howe’s medical cause of death was consistent with drowning.

There were no obvious marks, injuries or suspicious circumstances.

A letter from the solicitor acting for TEWV read out at the hearing said the trust accepted that the security protocol for observation was not followed.

Giving evidence, ward manager Valerie Murphy said: “If the lounge doors were open then a member of staff should have been in the lounge at all times.

“If they had to leave the doors should be locked.”

With a “good record of safety,” the doors have never been highlighted as an issue in previous inspections.

CCTV in the facility was “not used to monitor patients’ whereabouts”, the hearing was told.

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Following Mr Howe’s death, the trust has implemented a “more robust policy and procedure” which focuses on “making sure that training and briefing is not just about what staff do. It is about the people that they will be looking after.”

The employment of two members of staff was also terminated and disciplinary procedures were put in place.

Executive director of nursing and governing Christine Stanbury said: “Any incident is tragic and the trust does apologise for the loss of Mr Howe.”

A jury recorded a narrative verdict.

Mr Donnelly said: “In the narrative I do have to reflect the failing to monitor. It is such a feature that I can’t ignore it.

“Mr Howe’s movements are subject to speculation. Quite how or why he got himself in the vicinity of Skinningrove we can only speculate about.

“In this particular case, I can’t think of any disputes of fact.”

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Giving the final verdict, the foreman of the jury said that there had been “cumulative failures” to monitor Mr Howe, who was born in Hampshire.

The jury also concluded that he was found drowned on Cattersty Sands near Skinningrove.

However, the evidence did not “disclose how, when or why he come to drown.”

It is the second case in recent months to highlight apparent failings over how checks on mental health patients are carried out.

Malcolm Thomas, a resident on the medium-security Newtondale ward at Roseberry Park, was found hanged on June 18 last year.

The 56-year-old had not been seen by hospital staff for almost eight hours despite being prescribed checks every half-hour.

A TEWV spokesman said: “It is important that we learn from serious incidents such as the tragic death of Mr Howe.

“The trust always carries out a full investigation and takes action to help prevent something similar happening again.

“Although the issues raised by these two deaths were quite different we have learned from both incidents and have implemented a range of measures including strengthening our procedures and improving training for staff.”